As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Accordingly, much research on batteries satisfying various needs has been carried out.
Based on the construction of an electrolyte, a lithium secondary battery may be classified as a lithium-ion battery, a lithium-ion polymer battery, or a lithium polymer battery. The lithium-ion battery is a battery constructed in a structure in which an electrode assembly having a cathode/separator/anode arrangement is impregnated with a lithium electrolytic solution, and the lithium polymer battery is a battery constructed in a structure in which a solid electrolyte is used as the electrolyte such that the solid electrolyte serves as a separator. The lithium-ion polymer battery is a battery taking a middle position between the lithium-ion battery and the lithium polymer battery. Specifically, the lithium-ion polymer battery is constructed in a structure in which a cathode and an anode are coupled to a separator, and the coupling region thereof is impregnated with a lithium electrolytic solution.
Based on the shape of a battery case, the lithium secondary battery may be classified as a cylindrical battery, a prismatic battery, or a pouch-shaped battery. The cylindrical battery or the prismatic battery is a battery constructed in a structure in which an electrode assembly is mounted in a metal container. The pouch-shaped battery is a battery constructed in a structure in which an electrode assembly is mounted in a pouch-shaped case made of an aluminum laminate sheet.
One of the major problems to be solved in connection with such a battery is to improve the safety of the battery. For example, the lithium secondary battery may explode due to high temperature and high pressure in the battery, which may be caused by the abnormal operation of the battery, such as an internal short circuit of the battery, overcharge of the battery exceeding allowable current. and voltage, exposure of the battery to high temperature, dropping of the battery, or deformation of the battery due to external impact.
Consequently, a matter which must be essentially considered when developing the lithium secondary battery is to secure the safety of the battery. Various attempts have been made to secure the safety of the battery. For example, Japanese Patent Application Publication No. 2005-285429 discloses a secondary battery, having a nonaqueous electrolyte, constructed in a structure in which heat shrinkage resin is used as a means for applying shear stress to an anode current collector having a region where an anode active material is not formed, and the part of the anode current collector opposite to a cathode active material, in the region where the anode active material is not formed, is weakened when an aluminum-lithium alloy is formed, during the overcharge of the battery, whereby the current is interrupted by cutting the part. However, the above-described technology has a problem in that the overheating of the battery continues until the Al—Li alloy is formed, and the interruption of current introduced from the outside of the battery is possible only after the alloy formation region is sufficiently formed, and therefore, the current collector is cut, whereby it is not possible to secure the reliable operation of the battery.
Also, Japanese Patent Application Publication No. 2003-243036 discloses a cylindrical secondary battery constructed in a structure in which an insulation layer, made of a heat shrinkage material, is disposed between a core and a cathode or anode current collecting ring, and the core and the current collecting ring are brought into contact with each other, when the battery is abnormal, whereby electrode current flows, and therefore, the current in the electrodes is interrupted. However, the insulation layer is meaningful only for a cylindrical battery constructed in a structure in which it is difficult to mount a safety member to the outside of the battery.
On the other hand, Korean Patent Application Publication No. 2006-0054635 discloses a lithium secondary battery including a cap assembly, which has a safety bent and a current interrupting device, constructed in a structure in which the current interrupting device further includes a heat shrinkage film formed in a predetermined shape, one end of the heat shrinkage film is fixed between an outside ring and an insulation ring, the heat shrinkage film has a cutout part of a predetermined shape to allow a bimetal to contact the safety bent, and the heat shrinkage film insulates the bimetal and the safety bent when the temperature of the battery is increased. According to this technology, however, the bimetal and the safety bent are insulated by the heat shrinkage film, with the result that, when any one of them malfunctions, the operation of the battery is not performed. Furthermore, the inclusion of the bimetal and the safety bent complicates the manufacturing process and increases the manufacturing costs.
Consequently, there is a high necessity for a device to rapidly and sensitively interrupt external charge current when the abnormality of the battery occurs.